In recent years, drug-eluting implantable medical devices, such as, for example, stents, stent grafts, anastomosis devices, vascular grafts, vascular patches, AV shunts, catheters, guide wires, balloons, and filters, have gained more and more acceptance in the medical device industry as an effective means for controlled and sustained local drug delivery. These implantable medical devices, or at least portions thereof, are typically formed of or coated by a biocompatible polymer (either biostable or biodegradable) that encapsulates or otherwise contains one or more therapeutic drugs. In this manner, the therapeutic drugs are confined in or on the surface of the implantable medical devices by the biocompatible polymer and can be slowly released into the surrounding environment in a controlled and sustained manner.
Injectable formulations that contain drug-eluting nano-particles and/or micro-particles have also been successfully used for controlled and sustained local drug delivery. These nano-particles and/or micro-particles are formed by at least one biocompatible polymer with at least one therapeutic agents encapsulated therein. The biocompatible polymer is preferably biodegradable, but it can also be biostable. After injecting the nano- and/or micro-particles into a target site in the body, the encapsulated therapeutic drugs are released from the particle surfaces in a controlled and sustained manner, thereby achieving a prolonged and high local drug concentration at or near the target site.
Stability of the therapeutic drugs contained by the above-described implantable devices or nano/micro-particulate formulations has a significant impact on the drug release kinetics of such devices or formulations. In other words, the drug release kinetics may vary widely, depending on the stability of the therapeutic drugs contained therein.
There is therefore a need for improved drug-containing polymeric compositions with improved drug stability, which are suitable for forming drug-eluting implantable medical devices or drug-eluting nano- and/or micro-particulate formulations.